An infrared sensor has been widely used in a sanitary apparatus such as an automatic faucet, an automatic flushing urinal, a toilet closet flushing apparatus, a toilet seat with hot water ejection, a hand dryer, a toilet closet provided with a hot fan, and the like.
Most of traditional infrared sensors generally employ an active infrared sensing manner. That is, an infrared transmitter emits infrared rays with a certain wavelength, which are reflected by the body of a person and then received by an infrared receiver, for determining an intensity of the reflected signal to achieve an automatic sensing determination. However, for some materials (such as black clothes, hair, etc.) having a low reflectivity with respect to infrared rays, it is quite difficult to achieve an automatic sensing determination. After the infrared rays from the infrared transmitter are reflected by said materials, only little infrared rays can be received by the infrared receiver. Due to an insufficient intensity of the reflected signal, the sensor cannot determine whether or not there is an object, and thus fails in sensing.
In order to solve the above-mentioned problem of failure in sensing with respect to the traditional infrared bathroom product, a distance detecting sensor (PSD) is introduced into the field of automatic sanitary & bathing devices. As shown in FIG. 9, the PSD sensor is a photoelectric element sensitive to a position of an incident light. That is, when an incident light is irradiated to different positions of the light-sensing surface of a device, the PSD will output different electric signals. The PSD sensor utilizes the triangulation measuring principle, with a character of precise distance measurement, to achieve the automatic sensing determination. As shown in FIG. 9, the lights emitted from the light source, after being focused by the lens L1, are projected to the surface of the object to be detected. The reflected lights are focused by the lens L2 onto a one-dimension PSD to form a light point. Assuming that the distance between the centers of the lens L1 and L2 is b, the distance from the lens L2 to the PSD surface (i.e. the focal distance of the lens L2) is f, and the distance from the light point focused on the PSD surface to the center of the lens L2 is x, according to the characteristics of the similar triangles PAB and BCD, it can be concluded that the distance to be measured DIS is: DIS=bf/x. Therefore, if only the value of the position coordinate x of the light point on the PSD is measured, the distance of the object to be detected can be measured.
When it is detected that the distance of the object to be detected is within a predetermined range, the distance detecting sensor controls the operation status of the sanitary product, such as water-discharging, water-flushing, etc. As the distance detecting sensor achieves a purpose for automatic sensing by determining the distance between the object and the distance detecting sensor, rather than determining the intensity of the emitted signal, the defect of “failure in sensing due to an insufficient intensity of the reflected signal” in the traditional infrared-sensing means can be effectively solved.
However, for the sensor used in the sanitary & bathing industry, such as a sensitive faucet and a sensitive urinal, it is required that the sensor should have a relatively smaller volume to facilitate applying the sensor to the faucets or other sanitary & bathing products with various shapes. This is a special requirement for the sensitive sanitary & bathing products. For the above-mentioned distance detecting sensor, in this type of sensor where a focusing lens is used, it is necessary to take the problem of focal distance into account. If the detecting distance is longer, it is inevitably required that the lens should have a relatively larger diameter and thus a longer focus distance. In the common way, the infrared transmitting tube and the infrared receiving tube are welded directly on the traditional circuit board to face the lens, resulting in that the sensor box has a relatively large overall height and a relatively large volume as a whole. In this case, it is required to make a relatively large housing for the sensor accordingly, thus substantially limiting the appearance of the faucet or the sensitive urinal. Therefore, a problem to be solved is how to effectively control the size of a sensor having lens, such as a distance detecting sensor.